Patent GB-1137174-A (GB)
Title: Improvements relating to the control of light signalling installations
IPC: G08G1/082
Filed: 1966-10-12
Abstract: 1,137,174. Traffic - signal control. ZELLWEGER Ltd., USTER FACTORIES FOR APPARATUS AND MACHINES. 12 Oct., 1966 [1 Nov., 1965], No. 45595/66. Heading G4Q. [Also in Division H1] Light signalling installations such as roadtraffic signals are controlled in co-ordination by means of impulses sent over the power mains, preferably at audio-frequency, correcting signals being developed for establishing or maintaining the correct phase relationship between the impulses. Fig. 1 shows traffic signal installations A, B controlled from a master time-base 111 and pulse-generator 110 over power mains 1. Each installation comprises a time-base generator 2<SP>1</SP> feeding a generator 10<SP>1</SP> which produces pulses at desired instants in the cycle for operating the light signals 4<SP>1</SP>, 5<SP>1</SP>, 6<SP>1</SP>, 7<SP>1</SP> via a control circuit 3<SP>1</SP>. Impulses from the master generator are received at 8<SP>1</SP> and compared in phase in unit 9<SP>1</SP> with the generator 2<SP>1</SP>, the output being fed to the generator 10<SP>1</SP> to control the timing of the light signals. The pulses generated in the master unit 11 can be obtained from a master clock or from the mains frequency. The unit 11 can supply additional pulses to control the duration of the individual lights 4<SP>1</SP>-7<SP>1</SP> and these may be different in units A and B. The phase correction should be arranged to maintain each green phase above a predetermined minimum duration, e.g. by arranging that the duration of each phase is increased by the phase correction, not shortened, and the correction is extended over several cycles to avoid unexpected change-overs. The operation of units A and B, and successive units, can be arranged to provide a progressive green wave of predetermined velocity, which may be varied. The receivers 8<SP>1</SP> and 8<SP>11</SP> then have several outputs responding to different input pulses. Fig. 3 shows one unit such as A. A synchronous motor 80 drives the control member 3 through shafts 41, 42, 43, 44 interconnected by differentials 26, 27 and a clutch 20, the differentials normally being locked by stationary shafts 46, 40. When an impulse is received at 8, a signal is passed to a phase sensor 24 which compares the timing of the signal with the angular position of the shaft 42. If these do not correspond, a signal is sent to a coupler switch 22 which opens the clutch 20 and closes a clutch 19. The motor 80 now drives the differential casing shaft 46 rapidly until the shaft 42 is in its correct angular position relative to the received impulse. Another coupler switch 23 now compares the angular positions of shafts 42 and 44 and is energized by coupler switch 22 to close a clutch 21. The motor 80 now drives the differential casing shaft 40 to bring the shafts 42 and 44 into angular correspondence. In a modification (Fig. 6, not shown) the differential 26 is omitted and the shaft 42 is set into a predetermined initial position by a heart-shaped cam driven by an electromagnetic hammer operated by the received impulse. Slipping clutches prevent the shafts 41 and 44 from rotating while this is being done. Figs. 4 and 5 show how the angular positions of the shafts are compared with the timing of the impulse. A notched disc 57 is connected to the shaft 42 and in an incorrect angular position of the latter (as shown) the impulse arriving at 28 passes through the closed contacts 54, 55 to operate a relay 52 which holds on through contact 51. This relay closes the clutch 19 through contact 50 and opens clutch 20 through contact 49. When the angular position is correct the follower 82 enters the notch, contacts 54, 55 open and the relay drops out. The re-closing of contact 49 sends a pulse along line 30 which is differentiated and amplified to operate a relay 63 (Fig. 5) and close clutch 21 through contact 72. Shaft 44 drives a second disc 67 which has a projection 67 cooperating with a projection 58 on disc 53. If the shafts 42 and 44 are not in alignment (as shown) contact 66 will be closed and the relay 63 will hold on through contact 64. When the shafts 42, 44 become aligned the projections 58, 67 force the discs apart to open contact 66, deenergize the relay 63 and open the clutch 21. The notch 57 can be replaced by a cam profile.